Hot air heating furnace



Dec. 18, 1945.

J. C. MILES HOT AIR HEATING FURNACE Filed May 21, 1942 2 Sheets-Sheet 1 INVENTOR.

5 w M r 4y 5 F u w 5 Dec. 18, 1945. .L-c. MILES HOT AIR HEATING FURNACE 2 Sheets-Sheet 2 Filed May 21 1942 INVEN TOR.

JAMES C MIL 5 Fig. .5

Patented Dec. 18, 1945 UNITED STATES PATENT OFFICE HOT HEATING FURNACE James C. Miles, Cleveland, Ohio Application May 21, 1942, Serial No. 443,949

6 Claims.

This invention relates to heating devices and more particularly to a coal burning warm air furnace of a type suitable for use in private dwellings and in similar installations.

In coal burning warm air furnaces of comparable capacity heretofore used, the ratio' of the heating surface to the grate area was usually 15 or 20 to I, while the fire travel was normally about 5. /2 feet, and the resulting eificiency as measured by the ratio of the heat output to the heat input was about 55%.

An object of this invention is to provide a furnace of this type which will be highly efficient in operation and. economical in its use of fuel. I obtain this result by a novel construction and. arrangement of parts whereby a high degree of heat transfer is obtained.

Another object of this. invention is to provide a construction for such a, furnace wherein all of the structural parts may be simple, sheet metal stampings which may be economically manufactured. and assembled, castings being used only for the grate bars, and firebox linings.

A further object is to provide an arrangement such that the overall dimension of the furnace shall be at a minimum, the resulting simple, rectangular shape allowin the furnace to. be installed in a very limited space, as for instance, in a. small utility room on the first floor of a home not provided with a basement. When used in connection with a blower as illustrated in the embodiment herein described, a highly satisfactory and. economical heating system is provided.v

Other objects and features of the inventionwill become apparent upon an examination. of the accompanying drawings and specification and appended claims.

In the drawings,

Fig. 1 is a central vertical section through afurnace of my invention, the plane of the section being indicated by the line l--l on Fig; 2;

Fig. 2 is a front elevation of the furnace shown in Fig, 1;

Fig. 3 is a transverse, horizontal section taken on the line 3-3 in Fig. 1',

Fig. 4 is a perspective view of the inner unit of the furnace, and.

Fig. 5 is a rear elevation of the unit of Fig. 4.

Referring to the drawings, it will be noted that the inner unit or furnace proper is a simple, generally rectangular box [0, preferably of welded construction, the front I l and two sides l2 of which may be formed, as illustrated in Fig. 3, of a single plate. The. rear edges of the sides It may be curved at their central regions, as best seen in Fig. 4', and to them is attached, as by welding, a rear plate l3 which thus provides acurving roof for the combustion chamber C,

The front of the unit is of a double wall construction. As best seen in Fig. 1, the front plate II is provided with three openings l4, l5 and I6 for the ashdoor, firing door, and clean-out door l7, l8 and 19, respectively. Forwardly extending rims or lips may be formed on the plate l-l about the openings and to the rims 2:0 are attached, as by welding, similar rims 2| formed on an outer plate 22.

The region between. the ash door I! and the fire door l8 comprises a fire-box F which is provided with a lining which may embody four castings which interlock at their corners as shown in Fig. 3. The front liner 3!! and rear liner 3| are provided near their bottoms with bearings for the shaker bars. 32, which, together withprojections 33 on the side liners 34, comprise the floor of the firebox.

A feature of the present invention is, the novel form of fire tubes which I employ. As best seen in Figs. 1 and 3,v each fire tube, of which two are employed in the present embodiment, comprises two metal stampings and 4|, welded together at their junctions, and so formed as to provide a tubular passageway, preferably oval in cross section. The tube so provided is formed as along curving U, the legs of which are concentric with the curve of the rear or back wall [3 of the combustion chamber C and the two open upper ends of which are in communication with the combustion chamber at 99 and with the smoke chamber above it, at I! respectively. The great length of the fire tubes allows the maximum amount of heat to. be transferred from the burning flue gases to the circulating air which is introduced at the bottom, as will be hereinafter described.

An, additional feature in connection with the fire tubes is shown in the drawings, wherein the longer axis of the elliptical or oval cross section of the tube is at first oriented, a at 42, in a direction front-to-back of the furnace and where at the bottom 43 of the U there is a transition zone in which the oval is turned through a right angle so that the longer axis extends in a transverse direction, as at 44.. This formation of the tube is then carried to a point somewhat above the centerof the second leg of the tube where another transition zone 45 is reached and the oval is turned through a right angle to its former orientation at 46. This design effectively increases the heat transfer, for it will be noted, in Fig. 3, that ther is provided a large air passageway immediately adjacent the back wall of the combustion chamber and the inner leg 42 of the U, and that the lower portion 44 of the outer leg presents an effective barrier to the rising air stream, due to the end-to-end arrangement of the ovals of adjacent tubes, so that th air is caused to remain in contact with the hottest portions of the system. The return of the oval to the front-to-back position at the upper portion 46 of the outer leg then allows the free passage of the air to the upper plenum or distribution chamber. Air which rises at the rear of the pontion 44 may be maintained in close contact therewith by a diverter plate 41,

shownin Fig. 1. V

I preferably form the tube so as to maintain the same cross sectional area throughout its length.

Thus, for instance, a tube which starts with a sections of lighter guage than the box previously described. As best seen in Fig. 3,-each side 60 of this shell may be bent at its front and rear edges so as to provide portions GI and 62 of the front and back of the shell, respectively. The free vertical edges of the front portions GI are preferably provided with lips 83 which engage the free edges of the front plate 22. The rear portions 62 may be provided with curled edges 64 for engagement with inturned flanges 65 on the rear plate 66 which may thus be made removable if desired. The side plates are of double wall construction so as to provide dead air spaces 61 and 68 for proper insulation of the furnace. To this end, I have arranged inner plates 69 at the front of the shell in the region adjacent the inner unit and extending the full height thereof. These inner plates may be welded to the front portions GI and the side plates 60 as illustrated in Fig, 3. In addition to the plates 69, I provide plates 10 at the rear of the shell, adjacent the fire tubes and terminating at II adjacent their return bends 43. These plates may .be welded to the sides 60 and rear portions 62 and, as will be seen in Fig. 3, they extend inwardly to a point immediately adjacent the fire tubes. The plates I thus serve the double function of providing the dead air spaces 68 and confining the upwardly moving air-stream to the immediate vicinity of the fire tubes.

Surmounting the shell just described, I provide a plenum or bonnet 50, previously mentioned, from which the various risers of the distribution system lead.

The furnace of this invention may be employed in a warm air convection system. I prefer however to utilize a blower or fan, shown in Fig. 1 as communicating with the air-inlet opening 8| in the rear plate 66 of the shell. A portion of the air thus drawn from the surrounding atmosphere, or from a cold air return duct is forced into the shell, or heating chamber of the furnace and to impinge against the fire tubes, from whence it flows into the plenum and distribution system.

IA. part of the incoming air under pressure is forced into the ash-pit A and thence upwardly Th damper may be actuated, through a linkage 93, by an expansible bellows 94 which is in communication, as at 95, with a coiled tube 96 in the plenum 50. fluid so that the bellows is rendered responsive to the temperature of the outgoing air and moves the damper to regulate the amount of forced draft according to heating requirements. A temperature control of this general type is illustrated in Letters Patent Number 2,164,882 issued to me on July 4, 1939. j

The smoke chamber I00, heretofore referred to as being in communication with the outlet of the fire tubes, is a sheet-metal box mounted upon the combustion chamber C and provided with oval openings IOI into which the upper ends of the fire tubes are inserted. The smoke chamber terminates atan opening in one of the side plates 60, to which is fitted a smoke pipe I02 for conduction of the smoke and fumes to the chimney.

. To prevent smoke from entering the roomwhen the firing door I8 is opened I provide a. vent or direct-draft damper I08 between the top of the combustion chamber'and the smoke chamber I00. This damper is normally closed but may be. automatically opened by means of a linkage which connects it with the firing door. This linkage may take any one of a number of forms, such as a rod and lever connection or the simple chain and pulley system shown in Figs. 2 and 4. As there shown a light chain I03 is secured to a bracket I04 on the firing door I8 and thence passesaround pulleys I05 to anarm I06 on the shaft I0'I of the damper I 08. Thus, when the firing door is opened the chain will be pulled so as to tip the damper into open position to allow the smoke and fumes to rise directly into the smoke chamber and thence to the chimney, without being restricted by the fire tubes.

For most satisfactory operation, I prefer to provide one convector tube for each one-half square foot of grate area. Then as the grate area or capacity increases, the number of convector tubes increases in direct ratio, wherefore, concentration of the hot gases is obviated, thereby overcoming the dif'ficulty.that is present in all conventional furnaces which have only one gas outlet from the combustion chamber regardless of the size or capacity of the grate. The dispersion of the hot gases through multiple outlets and into convector heating tubes permits uniform distribution of the heated gases and the decentralization of heat which tends to preserve the metal and thereby to prolong the life of the furnace.

A furnace made according to the present invention has resulted in a ratio of heating surface to the grate area of 30 to 1 and has provided a fire travel of approximately 11 feet and has resulted in an efficiency of as measured by the ratio of heat output to heat input. Additionally, the invention permits substantially all of th parts to be made of stampings (except the grate and the fire box linings immediately adjacent thereto) whereby the cost of the furnace is greatly reduced and the danger of leakage is reduced to a minimum.

The embodiment illustrated has ample capacity for the requirements of average small size homes. Should a furnace of greater capacity be desired the inner unit and the shell need only be made of greater width and additional fire tubes added side-by-side as desired.

I claim:

1. A hot air heating furnace having a body The tube contains an expansible forming a combustion chamber, and a smoke chamber superimposed thereon, the combustion chamber having a front, a back and side walls, the back Wall extending upwardly and forwardly and a housing forming a heating chamber in back of the combustion chamber, an air inlet at the bottom and an air outlet at the top of the heating chamber, a plurality of fire tubes each having one end thereof in communication with the combustion chamber and the other end thereof in communication with the smoke chamber, said tubes being disposed between the back wall of the combustion chamber and the housing, said fire tubes being shaped substantially complementary to that of the back wall and extending downwardly into the heating chamber for substantially the length of the combustion chamber and then upwardly to communicate with the smoke chamber, and each of said tubes having a cross section comprising a long and a short axis, the tubes being positioned so that at the upper ends of the tubes the long axis extends from front to back of the furnace and at the bottom of the tubes the long axis extends transversely of the furnace.

2. A hot air heating furnace having a body forming a combustion chamber and a smoke chamber superimposed thereon, the combustion chamber having a back Wall which extends upwardly and forwardly, a housing forming a heating chamber adjacent said back wall and having an air inlet at the bottom and an air outlet at the top thereof, a plurality of fire tubes disposed within the heating chamber and being shaped substantially complementary to the shape of the back wall and extending downwardly into the heating chamber for substantially the length of the combustion chamber and then upwardly to communicate with the smoke chamber, each of said tubes having a cross section comprising a long and a short axis, each tube being positioned so that at the upper ends of the tubes the long axis extends from front to back of the furnace, and at the bottom of the tubes the long axis extends transversely of the furnace and each tube having that portion of the back leg in which the long axis extends transversely of the furnace extending a substantial distance up the back leg before the long axis is turned so as to extend in front to back relationship.

3. A hot air heating furnace having a body forming a combustion chamber, a, housing closing the same and forming a heating chamber, there being a smoke chamber disposed above the combustion chamber, a fire tube disposed in the heating chamber and having one end thereof in communication with the combustion chamber at a point forwardly of the center of the combustion chamber, the combustion chamber having a back wall extending upwardly and forwardly, said tube being shaped substantially complementary to the shape of the back wall, and extending downwardly into the heating chamber for substantially the length of the combustion chamber and then upwardly to communicate with the smoke chamber, said heating chamber having an air inlet at the bottom and an air outlet at the top thereof, and said tube having a cross section comprising a long and a short axis, the tube being positioned so that at the upper end of the tube the long axis extends from front to back of the furnace and at the bottom of the tube the long axis extends transversely of the furnace.

4. A hot air heating furnace having a body forming a combustion chamber and a smoke 7 tubes disposed within the heating chamber and each having one end thereof in communication with the combustion chamber at a point forwardly of the center of the combustion chamber, said tubes being curved substantially complementary to the curvature of the back wall and extending downwardly into the heating chamber for substantially the length of the combustion chamber but not below the level of the grate therein and thence upwardly to communicate with the smoke chamber, and each of said tubes having a cross section comprising a long and a short axis, the tubes being positioned so that at the upper ends thereof the long axis extends from front to back of the furnace and at the bottom thereof the long axis extends transversely of the furnace.

5. A hot air heating furnace having a body forming a combustion chamber, the combustion chamber having a grate therein, a housing enclosing the combustion chamber and forming a heating chamber, there being a smoke chamber disposed above the heatin chamber, the combustion chamber having a back wall extending upwardly and forwardly, a fire tube disposed in the heating chamber and having one end thereof in communication with the combustion chamber at a point forwardly of the center of the combustion chamber and substantially at the upper extremity of the back wall, said tube being shaped substantially complementary to the shape of the back wall, and extending downwardly into the heating chamber for substantially the length of the combustion chamber and to substantially the grate level and then upwardly to communicate with the smoke chamber, and said heating chamber having an air inlet at the bottom and an air outlet at the top thereof.

6. A hot air heating furnace having "a body forming a combustion chamber and a smoke chamber superimposed thereon, the combustion chamber having a grate therein, the combustion chamber having a straight front wall and a curved .back Wall, the back wall terminating at its upper end at a point forwardly of the center of the combustion chamber so as to restrict the crosssectional area of the upper portion of the combustion chamber, a housing forming a heating chamber in back of the combustion chamber, an air inlet at the bottom and an air outlet at the top of the heating chamber, a plurality of tubes disposed within the heating chamber and each having one end thereof in communication with the combustion chamber at a point forwardly of the center of the combustion chamber and substantially at the upper extremity of the back wall, said tubes being curved substantially complementary to the curvature of the back wall and extending downwardly into the heating chamber for substantially the length of the combustion chamber but not below the level of the grate therein and thence upwardly to communicatewith the smoke chamber.

JAMES C. MILES. 

